Multiplying positive numbers always comes out positive, no matter how many there are. So you can forget about the positive ones.
Every two negative numbers in a multiplication produce a positive.
Another way to say that is: If the number of negative ones is EVEN,
the answer is positive, and if it's ODD, the answer is negative.
That monster product of eight numbers in problem #12 will be negative,
because there are an odd amount of negative factors in it.